Electrolytic process



W. E. GREENAWALT. ELECTROLYTIC PROCESS. APPLICATION FILED MAR.19. 1915.

1,340,826. ate tedMay18,1920.

WILLIAH E. GEEYZFJHAWALT. OF DENVER, COLORADO.

ELTEl CFTEZQLYTIC PROCESS.

specification of Letters Patent.

original application filed February its. 1914, Serial No. 820.496. Divided and this application filed March To all who). it may concern Be it known that 1, WILLIAM E. GREEN- AWAL'I, ircitizen' of the United States, residingin the city and county of Denver and State of Colorado, have invented certain new and useful Improvements in Electrolytic Processes, of which the following is a specification.

The invention has for its more immediate object the maintaining of the variable valent elements in an impure electrolyte at their lowest valency, and thus, to a very large extent, increasing the cathode efiiciency.

This process application may be considered a division of my pending application, hicrial No. 820,496, filed February 24:, 1914, and. like that application, will be described more particularly to the electrolysis of im pure copper sulfate solution, although it is not intended to limit it to this use.

in the electrolysis of impure copper solutions, as for example those obtained in leaching copper ores. there is al 'ays present iron sulfate, which injuriously affects the operation. Ferrous sulfate in the electrolyte is .not particularly harmful., but the ferric. sulfate is highly detrimentaix If a solution of copper sulfate, containing ferrous sulfate is electrolyzed, copper is deposited at the cathode while sulfuric acid and ferric sulfate are produced at the anode. as represented by the following equations;

The ferric sulfate, finding its way back to the cathode, combines with the deposited copper and is again reduced to the ferrous condition. thus representing a loss of efficiency. asrepresented by the equation;

lf, however, the ferric sulfate can be reduced at the expense of a comparatively clcap reducing agent, such as hydrogen sullid, copper sulfid, or perhaps even iron sulfid, then acid is regenerated, and the iron in the electrolyte loses its ability to combine Serial No. 15,583.

with the deposited copper, as shown by the equations;

Ordinarily the reducing agents will be confined to hydrogen sulfid and copper sulfid, as shown by equations 4 and 5. The iron sulfid, if used, may react with the acid to form hydrogen sultid, as shown by equation 7, and the hydrogen sulfid may then Patented May 18, 1920. v

react with the ferric sulfate as shown by equation 4, or the reduction may take place as shown by equation 6. i

The sulfid reducing agent may be derived anda 'mlied in various ways. If hydrogen sulfir is used, the hydrogen sulfid is readily produced by reacting on .iron matte with sulfuric acid. If copper sulfid is used, it is preferably obtained by precipitating copper from its sulfate or chlorid solutions, with hydrogen suliid and applying the resulting copper sulfid' to the electrolyte. (opper matte, preferably high in copper and low in iron, can effectively be used, or, if native chalcocitc is available, that may be used.

Ordinarily hydrogen sulfid will be used as the reducing agent and applied in excess so that copper sulfid-will be precipitated. and the copper sulfid will then act as the reducing agent. Preferably also, the copper sulfid should be very finely divided so that agitation will keep it suspended in the electrolyte, and thus give the maximum I effect. (,oppcr matte may be used in large pieces. but it is preferably finely ground before applying. In any event, the cop er sulfid or matte would not be used as an e cotrode. but simply as a reducingagent, to reduce and maintain reduced, the injurious variable compounds in the electrolyte.

Referring to the accompanying drawing, Figure i represents a longitudinal section of a preferred apparatus for carrying out the process whcp either hydrogen sulfid or finely divided copper sulfid. or both, are made the reducing agents. Fig. 2 is a modified arrangement if copper sulfid-or matte is to be used in large pieces, or in bulk form.

In the figures, 1 represents a tank containing the electrolyte, which may be presumed to be copper sulfate solution as obtained from leaching copper ores, and neoessarily containing soluble salts of iron. 2 are the anodes and 3 the cathodes. 4 is a frame having stirring bars 5, interposed between the electrodes, if it is desired to stir the electrolyte. This frame reciprocates, as a whole, and is suspended from the track 6 by the rollers 8 and is moved by the mechanism 7.

10 represents a mechanism, taken as a Whole, by means of which the gas, say hydrogen sulfid, is. brought into a minute state of subdivision, or atomized, in contact with the electrolyte, and consists preferably of a tube, hood, or cylinder, 11, having perforations 12, in its periphery, or in disks 12 suspended in the solution, or electrolyte, by the shaft 13, from the ball bearings 14. This cylinder, or hood, is made to revolve at a high speed, driven by the motor 16.

The gas is preferably produced in the hydrogen sulfid generator 17, from iron sulfid and dilute sulfuric acid, and, by means of the compressor 18, is forced, with air, through the pipe 19, and into the atomizer 10, and into the revolving cylinder 11 through the stationary nozzle 19.

.It is desirable to maintain a circulation of the electrolyte. It may also be desirable to agitate the electrolyte. The idea is to bring a large volume of the solution in contact With the gas for the reduction of the variable valent salts, and then bring a large volume of the reduced solution in contact with the electrodes, and to prevent, as far as possible, the variable valent elements from being oxidized to the higher valencies.

To accomplish this, it ispreferred to apply the hydrogen sulfid in excess of that required to reduce the variable valent salts, so

that some copper sulfid will be precipitated, according to the well known equation:

This precipitated copper sulfid will then, in turn, act as'a reducing agent for the variable valent salts, as shown by equation 5. The copper sulfid so obtained is finely divided, easily agitated and kept in suspension, and

thus offers the maximum effect, as a reduc-.-

zle 19,'is trapped by the hood or cylinder,

and, as the pressure accumulates, it forces its way out of the perforations 12. As the cylinder and perforations are revolving at a high speed, the gas is distributed in exceedingly small subdivisions, or atomized, in contact with the solution. By regulating the speed of rotation, the amount and dilution of'the gas, and the volume of the electrolyte, the variable valent salts may be readily reduced without chemically precipitating any more copper sulfid than is desired, with the hydrogen sulfid.

The air and gas ascending through the apparatus 10, acts as an air lift and raises the level of the solution in the atomizer above the level of the electrolyte in the tank, proper, from which it is flowing, and thus permits of its being circulated, as shown at 1", or of its being-introduced into the next tank, as shown at 1 In either case the amount of ferric sulfate in the electrolyte may be kept so low as to be quite harmless.

The space in the upperportion of the atomizer 10 isinclosed, as shown by 28, so as to collect the excess gas, should there be any, which may then be conducted outside of the building, but it is preferably returned to the gasometer 17, through. the pipe 22, and again enriched in hydrogen sulfid, thus avoiding any waste of gas, while at the same time it is prevented from becoming a nuisance, as it would be if allowed to escape indiscriminately.

In Fig. 2, instead of using hydrogen sulfid, or copper sulfid precipitated with hy drogen sulfid, matte, or fused copper sulfid may be used, and introduced into the electrolyte. This maybe effectively accomplished by circulating the electrolyte-through the matte ,or by moving the matte through the electrolyte The result, in either case is much the same. The perforated anodes 2,

are suspended from a bar 36, and from flexible suspenders 25, and oscillated by the mechanism 7. The matte, 32, or fuse'd copper sulfid, is placed on top of the anodes and moves through the electrolyte, with the I anodes. The action is further promoted by having chambers 31 at the-ends of the .electrolyzer filled with matte, or copper sulfid, 32, -through which the electrolyte is circulated to and from the electrodes. The filter 30, prevents precipitate and insoluble matter from the matte from gettin to the elevtrodes. The electrolyte, flowing out of the cell through the pipe 34, is delivered to the pipe 35, and to the pump 37, and returned to the cell through the pipe In this way the electrolyte may be circulated inklefiagitate it.

It will be noted that neither in Fig. 1, nor Fig. 2 is the matte or copper sulfid electrically connected with the electrodes, nor is it nitely, while the oscillating anodes serve to directly electrolyzed, .but is used primarily to maintain the variable valent salts at their lowest valency in the electrolysis of the copper solutions.

The preferred method of Operating the process, however, is to apply the copper sulfid in a finely divided condition, in the atom izer 10, where it is agitated and remains in suspension, and thus gives the maximum effect. The sulfid is prevented from getting to the electrodes by means of the filter 15, and 30, so that while the electrolyte is agitated with the copper sulfid, the clear electrolyte only passes to the electrodes, while the copper sulfid remains behind until it is used up. The air and gas pipe 19, connecting with the solution pipes 21, induces an effective circulation, and thus the ferric salts may be kept at any minimum standard by regulating the circulation of the electrolyte, and the circulation of the electrolyte is best governed by the air and gas supplied to the atomizer. The solution may be alternately passed through the electrolyzers and the reducers, as shown in Fig. 1, especially if the solution is high in copper and high in iron, to makesuccessive reductions advisable.

The action of the hydrogen sulfid under the conditions used in thisprocess is positive so that none of it is likely to remain unconsumed, and hence it may be used with perfect safety, but should any escape, it is taken care of by the hood 28.

In treating copper ores, there are usually a lot of dilute solutions resulting from washing the ore; such solutions are preferably precipitated with hydrogen sulfid, and the copper sulfid precipitate used in the atomizer 10, as the reducing agent; in which case, little, if any hydrogen sulfid need be applied. Similarly, extremely foul solutions may be precipitated with hydrogen sulfid and the precipitate used in the atomizer. In either case the precipitate is dissolved in the act of reducing the ferric salts, and goes into solution as copper sulfate, and in going to the electrodes it is decomposed into pure copper and sulfuric acid. From this itwill be seen that in an extraction plant, all the' copper may be obtained as the pure electrolytic metal. The copper sulfid will go into solution according to equation 2, and on electrolysis of the resulting copper sulfate,

pure electrolytic metal will be deposited,-and

sulfuric acid regenerated,according to equation 1. v D

It is evident that, due to the energetic action of the sulfid reducing agent, practically I all the iron is maintained in the ferrous co'ndition, and thus the ferrous iron. in being re-oxidized at the anodesyto the ferric condition. acts as a depolarizer, and hence tends to reduce the electromotive force required for the electrolysis. There is a compensadone by withdrawing the solution from the electrolyzer, filtering, or settling, the insoluble matter from the electrolyte, and then distilling the sulfur from the insoluble matter. The sulfur may in this way be made a valuable by-product. If the elemental sulfur is not desired it may be burned off as sulfur dioxid, but on the whole the sulfur is best used in the production of hydrogen sulfid.

If hydrogen sulfid is not introducedinto the atomizer 10, it will still be desirable to introduce the air to act as an air lift and agitator, and also to assist in circulating the electrolyte.

By regulating the circulation of the electrolyte, it is easy to regulate the amount of ferric salts in the electrolyte, and as a small amount of ferric salts is not particularly harmful, the process caneasily be maintained under effective working conditions.

If iron sulfid is used as the reducing agent, hydrogen and hydrogen sulfid will'be liber ated by the acid solution, and will act to reduce the ferric salts. If preferred, either of these gases may be used separately for the reduction, or either gas may be used in connection with copper sulfid.

I claim:

1. In the electrolysis of impure copper solutions the process which consists in precipitating copper sulfid from copper solutions, With hydrogen sulfid, and applying the'copper sulfid precipitate to the electrolyte as a reducing agent.

2. In the electrolysis of impure copper solutions the process which consists in precipitating copper sulfid from copper solutions, with hydrogen sulfid, applying the copper sulfid precipitate to theelectrolyte as a reducing agent, and agitating the electrolyte impoverished in copper returning it to the ore.

4. In the electrolysis of copper solutions containing salts of the variable valent elements, the process which consists in reducing the variable valent salts to their lowest valency with hydrogen sulfid, and then maintaining them reduced with copper 5. In the electrolysis of copper solutions containing salts of the variable valent elements, the process which consists in applying copper sulfid to the electrolyte as a reducing agent, said copper sulfid not being electrically connected with either electrode.

6. In the electrolysis of copper solutions obtained from leaching ores and containing salts of iron, the process which consist in segregating a .portion of the electrolyte out of contact with the electrodes, applying copper sulfid to the segregated electrolyte, agitating the segregated electrolyte in the presence of the copper sulfid, separating the excess of copper sulfid aid the resulting liberated sulfur from the segregated electrolyte, and repeating the cycle of deposition and reduction if necessary, and then when a the electrolyte is sufliciently impoverished in copper returning it to the ore.

7. In the electrolysis of a solution of a metal salt of a po'lybasic acid obtained from,

. leaching ores and containing salts of the variable valent elements, the process which consists in applying a reducing gas to the solution to reduce the salts of the variable valent elements from a higher to a lower valency, and then continuing the reduction of the .higher valency salts formed by the electrolysis by means of concentrated copper sulfid, and thenwhen the solution is sufficiently impoverished in the metal being deposited and regenerated in acid returning the solution to the ore.

8. In the electrolysis'of copper sulfate solutions obtained from leaching ores and containing salts of iron, the process which consists in ap lying copper sulfid to the electrolyte in a nely-divided condition'to reduce the ferric sulfate formed by'the electrolysis to the ferrous sulfate so that the solution is returned to the ore in the ferrous condition.

9. In the electrolysis of copper solutions obtained from leaching ores and containing salts of the variable valent elements, the process which consists in applying a sulfid reducing agent to the electrolyte to reduce and maintain reduced the 'variable vvalent elements at their lowest valency during electrolysis, so that the solution may be returned to the ore in a reduced condition.

10. In the electrolysis of copper solutions I the process which consists in applying finely dividedcopper sulfid to the electrolyte as a reducing agent, agitating the electrolyte in the presence of the finely divided copper sulfid so that the variable "valent salts are -in a substantially reduced condition when the solvent is again applied to the ore.

- 11. In the electrolysis of impure copper solutions obtained from leaching copper ores and containing salts of the variable valent elements, the process which consists in reducing the variable valent salts from their higher to their lower valencies produced in the electrolysis, with an insoluble compound capable of reacting with the variable valent elements but incapable of reacting with the regenerated acid, so that the solution may be returned .to the ore in a reduced condition.

12. A process which consists in leaching ores of copper with an acid solution to disand then returning the solution to the ore insubstantially a reduced condition.

13. A process which consists in treating ores of copper with an acid sulfate solution, subjecting the resulting copper sulfate solution containing salts of iron to the action of electrolysis to deposit the copper and regenerate the solvent, maintaining the iron salts. in the solution in substantially the ferrous condition by the action of copper sulfid not electrically connected with either electrode, and then returning the regenerated solution to the ore with the iron in substantially the ferrous condition.

14, A process which consists in treating ores of copper with an acid sulfate solution to dissolve the copper from the ore, subject ing the resulting copper sulfate solution fate solution to the ore with the iron in sub-,

stantially the ferrous condition.

15. In the electrolysis of a solution of a containing salts of iron to the action of elecv salt of a polybasic acid containing salts of the variable valent elements, the process which consists in introducing into the solution a precipitated sulfidreage'nt capable of reducing the salts of the variable valent elements from a higher to a lower valency.

16. In the electrolysis of a solution of a salt of a polybasic acidobtained'from leaching ores of metals and containing salts of the variable valent elements, the process which consists in precipitating co per from its solutions" with hydrogen sulfi and apply-ing the copper sulfid precipitate to the electrolyte to reduce thehigher valencysalts formed by the electrolysis to alower valency.

17. In the electrolysis of a solution of a metal salt of a polybasicacid obtained from leaching ores and containing salts of the variable valent elements, the process which consists in reducing the higher valency salts formed by the electrolysis to a lower valency by means of copper sulfid, and then 'when the solution is sufiiciently impoverished in metal returning the solution to the ore.

18. In the electrolysis of a solution of a metal salt of a polybasic acid obtained from leaching ores and containing salts of the variable valent elements, the process which consists in repeatedly reducing the higher valency salts formed by the electrolysis to a lower valency by means of copper sulfirl,

and then when the solution is sufficiently impoverished in metal values" and regenerated in acld returmng the solution to the ore.

19. In the electrolysis of a solution of a metal salt of a polybasic acid obtained from leaching ores and containing salts of the variable valent elements, the process which consists in reducing the higher valency salts formed by the electrolysis to a lower valency by means of concentrated copper sulfid, and then when the solution is sufficiently impoverished in the metals being deposited and regenerated in acid returning the solution to the ore.

WILLIAM E. GREENAVVALT.

Witnesses:

WILBER C. THOMAS, ALIcE E. Ross. 

